1. Field of the Invention
The invention relates to an apparatus for a cardiological therapy, in particular to an ablation apparatus, consisting of an ultrasonic transducer and an applicator adjacent to the transducer for providing an endocardial energy output.
2. Description of the Prior Art
Ablation apparatuses serve to eliminate disturbances in the heart rhythm by means of electrocardial operations. With known apparatuses the heart tissue is heated locally to such an extent that only the electrical properties of the tissue are damaged. A high frequency generator (e.g. Osypka HAT200S, HAT300, Medtronic Atakr, EPT 1000) is often used as an energy source for the ablation. Ultrasound and microwaves can also used as energy sources. Furthermore, an ablation can also be performed by undercooling or by means of chemical substances. These two intervention possibilities are also included here in connection with the term "energy output".
The energy output is advantageously regulated by means of a temperature measurement performed at the applicator. This regulation serves to prevent a coagulation of the tissue as well as of the blood and thus the formation of thromboses.
WO 95/17131 describes a catheter and a method in which the position of the catheter relative to the tissue can be determined by means of ultrasound. The goal is to give off the energy only when the catheter is in a suitable orientation relative to the tissue and is in direct contact with it. The energy can thus be introduced into the tissue with a good efficiency; an unnecessary and damaging output of energy to the blood is therein avoided.
As is known, the thickness of the myocardium can be measured echocardiographically by means of ultrasound (see e.g. J. H. Myers et al. "Direct Measurement of Inner and Outer Wall Thickening Dynamics with Epicardial Echocardiography", Circulation, Vol. 74, No. 1, Jul. 1986, pages 164 ff.). Tissue dimensions, and in particular myocardium thicknesses, can be determined using most of the picture producing ultrasound devices.
In the case of frequent disturbances in the heart rhythm, such as for instance auricular fibrillation, it is important that the electrical properties of the myocardium are thoroughly destroyed in depth so that no further excitation conduction can take place in the treated tissue. The elimination of fibrillation in particular, which results in chaotic excitations, means that it is in many cases difficult to assess the success of the ablation in an electrical manner.